The present invention relates generally to passive security systems, and more particularly to a passive remote keyless entry system for a vehicle.
Remote Keyless Entry (RKE) is being installed at an ever increasing rate in automobiles. The dramatic rate of installation is being fueled by consumer acceptance and subsequent demand of RKE systems. Additional improvements in RKE system technology are possible and are even being requested by the consumer. The problem of fumbling for the existing active RKE FOB while standing in the rain or when in an emergency situation has provided the motivation to design and implement a passive RKE system.
Existing passive RKE systems cause unintentional lock actuations when the consumer is in the near vicinity of the vehicle whose desires do not include unlocking the vehicle ("false alarms"). False alarms present an additional drain on the vehicle and FOB batteries, prematurely reducting the operating life of the locking system. They can also present a security issue if the false alarm leaves the doors unlocked.
Many RKE schemes have been investigated incorporating capacitive/inductive proximity sensors and optical sensors. Many problems are associated with such sensors in addition to the prohibitive cost. For example, optic sensors suffer from contaminants (i.e. dirt, grease, salt, etc.) causing the lenses (apertures) to become opaque to the optic energy. Thermal sensors suffer in that they are unsuitable for detecting gloved hands (if under the door handle) or wearing winter clothes.
The task is further complicated by the relatively long actuation time required for the lock motors/solenoids and mechanical linkage to change the state of the lock(s). This means the passive RKE system must "read the consumer's mind", at a distance far enough away from the lock (door) to allow sufficient time for the locks to unlock the door, without compelling the consumer to manipulate the door handle more than once.